Since the occurrence of fins requires after-treatment processes of a molded article, it decreases the working efficiency of the molding process and pollutes the environment undesirable.
In accordance with a convention molding method, especially in which a cavity is formed by connecting molds, the molds are pressed against each other in order that the melt does not spill through the parting portions when pouring, and the parting surfaces are formed as flat as possible, so that each mold may be connected completely.
But it is nearly impossible to produce an article without fins, because as the sand is bare along the parting lines, in case of pressing the molds too hard, the sand near the parting lines may be broken down into a cavity.